The thin-film magnetic head of a perpendicular magnetic recording method has a configuration which inputs a recording signal by perpendicularly magnetizing a hard film of a record medium. The thin-film magnetic head of a perpendicular magnetic recording method may narrow a required width to magnetize and transit so as to improve a recording density more than a thin-film magnetic head of a longitudinal magnetic recording method.
JP-A-2002-100006 discloses a record-reproducing complex-type thin-film magnetic head, a recording portion, and reproducing portion are overlapped in a film thickness direction. The thin-film magnetic head has a supplementary magnetic pole (return-yoke layer) that is disposed more rear from a medium opposed surface than a major magnetic pole, an upper shield, and a lower shield so as to prevent a magnetic field of the supplementary magnetic pole from being expanded and prevent an information stored in a record medium from being erased due to the magnetic field generated in the supplementary magnetic pole and the upper shield (see [0022] or [0025] of JP-A-2002-100006).
A magnetic record reproducing device disclosed in JP-A-2005-190515 (US2005141142A1) is formed shorter than a back contact that bonds an upper shield and a lower shield to a major magnetic pole and a supplementary magnetic pole (return-yoke layer) so as to suppress a magnetic flux flowing in the upper shield and the lower shield and lower a magnetic field applied to a reproducing element formed between the upper shield and the lower shield. In such a configuration, it is difficult for the reproducing element to be degraded or destroyed.
JP-A-2004-005826 improves an overwrite quality. In FIG. 1 of the JP-A-2004-005826, the cross-sectional view of a thin-film magnetic head is illustrated, but gaps of a height direction of the upper shield, the lower shield, a supplementary magnetic pole (return-yoke layer), and the like are not described.
Except for the case described above, when a floating magnetic field (disturbance-magnetic field) is absorbed by the upper shield layer, the lower shield layer, and the return-yoke layer, magnitudes of leakage magnetic fields leaked from each front end surface the upper shield layer, the lower shield layer, and the return-yoke layer toward a record medium increases. Accordingly, the erasing and the like due to the record data recorded in the record medium may be properly prevented.
It is preferable that the magnitudes of the leakage magnetic field leaked from each front end surface of the upper shield layer, the lower shield layer, and the return-yoke layer are as balanced and reduced as possible. For example, the magnitude of the leakage magnetic field leaked from the upper shield layer or the lower shield layer may be reduced so as not to affect the magnetic data. When the magnitude of the leakage magnetic field leaked from the return-yoke layer is large, the erasing cannot be solved. Accordingly, the magnitudes of the leakage magnetic fields of three magnetic layers are necessary to be as small as possible.
Conventionally, studies have not been conducted as to the magnitudes of the leakage magnetic fields leaked from each front end surface of the upper shield layer, the lower shield layer, and the return-yoke layer being as regular and small as possible. According to experiments, when lengths of the height direction of the upper shield layer, the lower shield layer, and the return-yoke layer are all equal and back end surfaces of each layer are formed on a location equal to the film thickness direction, the magnitudes of the leakage magnetic field leaked from the upper shield layer, the lower shield layer, and the return-yoke layer become unbalanced, in particular, the magnitude of the leakage magnetic field leaked from the return-yoke becomes large, and the record data in the return-yoke layer is easily erased.
In at least FIGS. 2 and 15 of JP-A-2005-190515 the and FIG. 1 of JP-A-2004-005826, the length of the upper shield layer, the lower shield layer, the return-yoke layer are not equal. In JP-A-2005-190515 and JP-A-2004-005826, specific lengths of the return-yoke layer, the upper shield layer, and the lower shield layer are not described and a length difference between the return-yoke layer and the upper shield layer is not obvious.